Create multiple Server Farms in one IIS ARR (Application Request Routing)

Most people use ARR to increase web applications' scalability and reliability by leveraging rule-based routing, load balancing, shared hosting and disk caching, etc. In my case, I found it a very good solution for medium sized corporations to expose their data via RESTful, OData or SOAP based web services if they already have the infrastructure in place and do not intend to go Cloud at the moment.

In our business scenario, there are a few implicit requirements:

1. We should be able to use existing infrastructure without adding new hardware/servers.
2. We should be able to expose all services using only one endpoint, which is the gateway. Furthermore, we expose the services as standard HTTP port 80 while the actual ports for our internal services are not disclosed.
3. We must have the least number of holes in firewall for all services, ideally the number would be one.
4. We should have a consistent and clean URL pattern for all services. For example: http://greatplace.org/Services/thisService?param1=x and http://greatplace.org/Services/thatService/, etc.
5. We may also use this gateway to expose other resources than web services, e.g. reports.
6. The server farms can support different authentications, e.g. reports farm does not allow anonymous access.
7. The solution must be reliable and easy to maintain though load balancing and redundancy are not big concerns at present.

A simple practical design is like this:

For big enterprises, multiple ARRs can be utilised for routing specific types of requests to different server farms, for example one ARR for reporting server farm and one for general web services, etc. But what I am sharing here is how to use one ARR to dispatch requests to multiple server farms based on rule-based routing.

So first we create two server farms, add servers (and port mappings if any) in each farm:

Then we add the URL Rewrite rules

For the Reports Farm, we would like the original URL http://internal.server.ip:port/Reports/Pages/Report.aspx?ItemPath=SomePath to be routed to the servers in the reports farm with the exposed URL being http://external.server.ip/Reports/Pages/Report.aspx?ItemPath=SomePath, so the rule is like:

For the Services Farm, we would like the original URL, e.g. http://internal.server.ip:port/Services/Service1/Odata.svc/Products(5) to be routed to the servers in the services farm with the exposed URL being http://external.server.ip/Service1/Odata.svc/Products(5), so the rule is like:

And there we go. We can then configure the load balance and caching stuff as usual. It's awesome that ARR provides such great flexibility and capability in IIS.

Ref:

1. ARR
2. Using the URL Rewrite Module